Recently much research has been undertaken in the geriatric field ranging from the physiology of aging to the design of drugs and pharmaceutical preparations to daily care and assistance. According to, inter alia, the silver science research conducted by the Japanese Ministry of Health and Welfare, there is an interesting research report entitled `Studies for the construction of new pharmaceutical preparations and new packaging containers optimal for administration to elderly subjects` (Masayasu Sugihara, Tokyo Women's Medical College, and others) (Aug. 22, 1989 issue of the Yakuji Nippo). By way of illustration, as such new preparations, a) buccal dissolution type preparations, b) paste-like preparations and c) jelly-like preparations are described. Particularly, buccal dissolution type and paste-like preparations are claimed to be easy for elderly persons to ingest and excellent in stability. The buccal dissolution type preparations, in particular, contain polyethylene glycol 1000 as the base which dissolves in the oral cavity and an oleaginous base as the base which melts at the temperature prevailing in the oral cavity and, in consideration of sensory factors such as taste and texture as well as moldability, further contain sucrose and mannitol. These are molded by filling the pocket of a vinyl chloride molding sheet for press-through package (PTP) use with a heat-melted medicated base and allowing it to cool and take form. In this manner, a buccal dissolution type solid preparation for elderly persons is manufactured.
Japanese Patent Laid-open No. 76420/1977 describes a method of manufacturing a porous tablet which features a high disintegration rate insuring rapid dissolution in the oral cavity which comprises placing a magmatic mixture or solution containing 5 to 80% by weight of an inert solvent freezing at a temperature of -30.degree. C. to 25.degree. C. and the balance of a tablet-forming composition in an inert cooling medium such as liquid nitrogen to cause solidification, then compressing the resulting granules into tablets at a temperature not higher than the freezing point of the solvent, and finally removing the solvent by freeze-drying or air drying.
Japanese Patent Publication No. 24410/1983 discloses a method of manufacturing a porous tablet with good disintegrability which comprises mixing a tablet-constituting composition with a solvent which is inert to said composition and freezes at a temperature of -30.degree. to +25.degree. C. (for example, water, cyclohexane or benzene), the proportion of said solvent being 5 to 80% by weight, placing the resulting mixture in an inert cooling medium for solidification, compressing the resulting solid into tablets at a temperature lower than the freezing point of said solvent and evaporating the solvent by freeze-drying or spontaneous drying.
Japanese Patent Laid-open No. 15830/1986 discloses an antacid composition having a porous and extra fine crystal structure which comprises an antacid and a base for confectionery comprising a sweetener for confectionery and a plasticizer.
On the other hand, in certain countries, there are guidelines (e.g. USA"FDA 1983) for research concerning pharmaceutical products for elderly persons and, as a buccal dissolution type solid preparation, Zydis from R. P. Scherer, England, is commercially available, for instance. While the composition of this preparation is not known, it is manufactured by blending an active ingredient with a polymer, sugar and other ingredients, dissolving the blend and freeze-drying the solution (Manuf. Chemist. Feb. 36, 1990).
However, from the standpoint of practical utility as buccal preparations, the conventional products described above are not fully satisfactory in shelf-life, solubility and the scope of compatible medicament. For Example, the composition described in said Japanese Patent Laid-open No. 15830/1986 is prepared by heating and melting the ingredients, so that it is inferior in the scope of compatible medicament and disintegratability of the preparation in the oral cavity. Also, Zydis (trade name) mentioned above has problems with the water solubility of the active ingredient, mechanical strength of the preparation, and % content of the active ingredient so that it is not satisfactory, either, for administration to patients of advanced age.
Furthermore, a tablet which disintegrates and dissolves quickly is generally weak in mechanical strength. Therefore, it has been considered necessary to develop a preparation which offers practically acceptable disintegration and dissolution speeds in the oral cavity and, at the same time, possesses a sufficient mechanical strength so that it will not be destroyed in the course of manufacture and subsequent distribution.